It's not that I don't like J. Staal, I do. But a couple of things.
Habs needs Plek, what we need to get rid of is David Desharnais if we're trading for a #2C... and in either case we need one more offensively inclined than J. Staal.
Right now down the middle we're Galchenyuk-Plek-DD or Galchenyuk-DD-Plek, we need to move DD+++ (big plus imo, overpayment even) to get a scoring #2C so that Plek can be moved to the 3rd line that way we not only have a defensively responsible #3C but one who can chip in some points.
After said trade we'd look a lot better:
Byron-Galch-Radulov
Patch-New #2C-Gallagher
Carr-Plekanec-Shaw (Shooter/two-way fwd/grinder)
Danualt-Mitchel-Flynn (Top 4th line atm)
Even if you do this, we need a top 6 LW.
Habs desperately need a #2C and a #2LW, if we can dump DD in the process of getting those two then great. Doesn't need to be somebody incredible, but competent will do.
tl;dr version: Habs need to move DD++++ (not plek) for a #2C and #2LW, even if it's a massive overpayment of futures. Habs made the Subban trade to win now, so it's time we overpay in prospects/picks to get it done.